After today’s signing, each country will take the agreement home and formally ratify it in processes dependent on their governments. In some, like the United States, it’s as simple as a leader declaring support. In others, such as Japan and India, the agreement will have to go through parliamentary houses. Some countries may even have to implement new laws.

Today marks a day of celebration; Leonardo DiCaprio and other celebrities will be present for the signing, which is expected to involve a great deal of pomp and circumstance. But we haven’t solved climate change yet. Some environmentalists worry the agreement isn’t strong enough. Chatham House senior research fellow Shane Tomlinson told the BBC, “For the Paris agreement to have any credibility we can’t afford to wait ten years in order to increase ambition.”